“Super-slugs” are invading British gardens – and we don’t know how to stop them

Mmmmmm, slimy. Image: Xauxa Håkan Svensson.

The Daily Mail calls it a “slime wave”. The Sun calls them “an army”. Either way, both papers have reported 500bn slugs are set to invade British gardens, after a mild winter created perfect breeding conditions. The Conversation

So is the UK really about to be overwhelmed by slimy slugs? The simple answer is no, but there could be something far worse in store.

Headline numbers alone aren’t necessarily something to get in a lather over. A typical garden can contain several thousand slugs, and the “500bn” figure is derived from estimates of maximum numbers per area. In any case, slug numbers can rise and fall a great deal across time and space, in natural cycles, and even astonishingly dramatic increases are not always cause for concern. Like waves crashing against a beach, the rise is often transient and local – usually slug numbers will drop back to normal, with the disturbance hardly noticed beyond a few local gardeners.

What is more problematic is the progressive, sustained and perhaps less spectacular rise in numbers which, tsunami-like, is maintained for far longer, and spreads widely throughout the countryside. This is Britain’s real slug invasion. So what can we do about it?

The trigger seems innocuous enough in isolation: a few non-native slugs from continental Europe have accidentally been introduced. Several of these species have close relatives in the UK, so similar in fact that only specialists can tell them apart, and they can interbreed freely. Of course, many animals can create hybrids without presenting a threat, but what makes slugs different – and these hybrids so worrying – is their interesting and deviant sex lives.

This is a hybrid between a ‘Spanish stealth slug’ and the UK’s common black slug. Image: Les Noble/author provided.

Slugs are hermaphrodites, which means the same individual exists as both sexes; they first develop as males, before experiencing a true hermaphrodite phase to become female. This means they can dispense with normal mating requirements, and this is where the consequences of the difference between British and continental species becomes significant.

Why British slugs are different

When slugs colonised the UK after the last ice age, they found an island recently covered with ice sheets, where the biological diversity remained poorer than continental Europe. In these circumstances, the ability to self-fertilise was a good evolutionary strategy, one which ensured reproduction even when slug populations were devasated by harsh weather.

A downside of such continued close inbreeding (and mating with oneself is as inbred as it gets) is a rapid loss of genetic variability, and some British slug species eventually came to consist of almost genetically identical individuals. This meant they were more vulnerable to parasites and pathogens that could rapidly evolve to overcome their defences.

Meanwhile, in continental Europe, slugs were becoming more diverse, as balmier weather meant parasites and pathogens were a bigger issue than finding a mate. These slugs tended not to self-fertilise, and were genetically highly variable. This made at least some of them more resilient to attacks from parasites – a possibility not afforded to the inbred British slugs.

Echoes of these different past environments resonate in contemporary species. British slugs, adapted to a variable climate and dearth of mates, have fallen into the clichéd “No sex please, we’re British” mould, producing fewer, bigger eggs later in life by self-fertilisation. Continental slugs, meanwhile, adapted to resist rapidly evolving enemies. Their strategy is therefore to produce many smaller eggs earlier in life, which maximises genetic diversity and compensates for losing many individuals to infection.

The ‘Spanish slug’, one of Britain’s key invaders. Image: tviolet/creative commons.

These different adaptations weren’t an issue until humans disturbed the natural order by moving slugs back and forth as stowaways in commercial produce. As a result of this, we’ve seen widespread breeding between British and continental species. These new hybrid “super-slugs” are highly fertile, and their genetically diverse offspring are adapted to cope with both the British climate and parasites and pathogens, most of which remain in continental Europe anyway.


Fighting the slug invasion?

Legislation aimed at environmental protection has led to the EU banning commercial use of molluscicides (pelleted chemicals which poison slugs but cause collateral damage to other wildlife). Instead, the emphasis is on using natural enemies like nematode worms, though these are generally ineffective against the larger invasive hybrids.

Nonetheless, the increased slug biomass could still host important veterinary or agricultural parasites and pathogens, spreading more plant and animal diseases. Remarkably, despite their obvious presence in our gardens, we remain startlingly ignorant of the fundamental biology of slugs; evidenced by recent work which increased the number of identified British species by more than a fifth.

So where are we going with this phenomenon? Studies have already found invasive slugs and snails can destabilise ecosystems and reduce biodiversity in the US and Scandinavia. Something similar is happening here in the UK.

The good news is that our research suggests population sizes do eventually begin to decline, after 30 to 40 years. The ecosystem may eventually rebound from this slug invasion, but it remains to be seen how long it will take and what the lasting effects will be for the spread of diseases, ecosystem services, or British biodiversity.

Leslie Noble is a reader in zoology at the University of Aberdeen.

This article was originally published on The Conversation. Read the original article.

 
 
 
 

What do new business rates pilots tell us about government’s appetite for devolution?

Sheffield Town Hall, 1897. Image: Hulton Archive/Getty.

There have been big question marks about any future devolution of business rates ever since the last general election stopped the legislation in its tracks.

Not only did it not make its way to the statute book before the pre-election cut off, it was nowhere to be seen in the Queen’s Speech, suggesting the Government had gone cold on the idea. (This scenario was complicated further recently by the introduction of a private members’ bill on business rates by Conservative MP Peter Bone, details of which remain scarce.)

However, regardless of the situation with legislation, the government’s announcement in recent days of a pilot phase of reforms suggests that business rates devolution will go ahead after all. DCLG has invited local authorities to take part in a pilot scheme which will allow volunteer authorities to retain 100 per cent of the business rates growth they generate locally. (It also notes that a further three pilots are currently in operation as they were set up under the last government.)

There are two interesting things in this announcement that give some insight on how the government would like to push the reform forward.

The first is that only authorities that come forward with their neighbours with a proposal to pool all business rates raised into one pot across a wider geography will be considered. This suggests that pooling is likely to be strongly encouraged under the new system, even more considering that the initial position was to give power to the Secretary of State to form pools unilaterally.

The second is that pooled authorities are given free rein to propose their own local arrangements. This includes determining, where applicable, a tier split (i.e. rates distribution between districts and counties), a plan for distributing additional growth across the pool, and how this will be managed between authorities.

It’s the second which is most interesting. Although current pools already have the ability to decide for some of their arrangements, it’s fair to say that the Theresa May-led government has been much less bullish on devolution than George Osborne in particular was, with policies having a much greater ‘top down’ feel to them (for example, the Industrial Strategy) rather than a move towards giving places the tools they need to support economic growth in their areas. So the decision to allow local authorities to come up with proposed arrangements feels like a change in approach from the centre.


Of course, the point of a pilot is to test different arrangements, and the outcomes of this experiment will be used to shape any future reform of the business rates system. Given the complexity of the system and the multitude of options for reform, this seems like a sensible approach to take. But it remains to be seen whether the complex reform of a national system can be led from the bottom up. In effect, making sure this local governance is driven by common growth objectives, rather than individual authorities’ interests, will be essential.

Nonetheless, the government’s reaffirmation of its commitment to business rates to devolution and its willingness to test new approaches is welcome. Given that the UK is one of the most centralised countries in the western world, moves to allow local authorities to keep at least some of the tax revenue that is generated in their area is a step forward in giving places more autonomy over how they spend their money. That interest in changing this appears to have been whetted once more is encouraging.

There are, however, a number of other issues with the current business rates system which need to be ironed out. Centre for Cities is currently working on a briefing of the business rates system, building on our previous work in this area, and we’ll be making suggestions as to how the system can be improved.

Hugo Bessis is a researcher for the Centre for Cities, on whose blog this article originally appeared.

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